The present invention relates to a hydraulic brake system comprising a pedal-actuated braking pressure generator which disposes of a feed tank and to which the wheel brakes are connected by way of pressure-fluid lines. The system further comprising an auxillary-pressure supply system with pump and pressure-fluid supply reservoir, and an auxilliary-pressure control valve which produces an auxiliary pressure proportional to the pedal force.
In a known brake system of this type, there is provision of a tandem master cylinder with a hydraulic brake power booster connected upstream thereof as well as an auxiliary-pressure supply system comprising a pump and a hydraulic accumulator. The hydraulic booster contains an auxiliary-pressure control valve which, on application of the brake pedal, causes an auxiliary pressure proportional to the pedal force and acting on the pistons in the master cylinder. The boosting factor of the brake system is selected by the ratio of the surfaces of a transmission piston in the interior of the brake power booster in relation of the surface of an actuating piston coupled mechanically to the brake pedal. As the brake circuits are designed as static circuits, the volume of the pressure chambers in the master cylinders must be adapted to the respective brake system.
Furthermore, slip-controlled brake systems are known wherein the hydraulic braking pressure generator is likewise composed of a master cylinder and a hydraulic brake power booster connected upstream thereof (for instance German printed and published patent applications Nos. 30 40 561 and 30 40 562). During slip control, dynamic pressure out of the auxiliary-pressure supply system will be introduced by way of the booster chamber into the brake circuits which are connected to the master cylinder and which are static until commencement of slip control. This way, the discharge of pressure fluid into the pressure supply reservoir during the phases of pressure reduction will be compensated. Such systems are rather complicated and costly.
Likewise, known are slip-controlled brake systems, the braking pressure generator of which are also composed of a hydraulic brake power booster with a master cylinder connected downstream thereof, and wherein on commencement of slip control dynamic pressure is metered out of the brake power booster directly into the wheel brake cylinders of the wheel connected to the master cylinder. To this end, the wheel brakes connected to the static brake circuits communicate by way of electromagnetically actuable multidirectional control valves with the master cylinder so that change-over of these valves causes interruption of the hydraulic connection between the master cylinder and the wheel brakes and permits connection of the auxiliary-pressure source instead of the master cylinder. During normal braking operations (i.e., without slip control) or until change-over of the solenoid valves, respectively, the circuits concerned are strictly static brake circuits.
It is an object of the present invention to develop a brake system which is simple and entails little effort and which system extends a slip-controlled brake system by insertion of electromagnetically controllable inlet and outlet valves and by equipment with a measuring and control electronics, and wherein dynamic pressure out of an auxiliary-pressure supply system is introduced into the pressure chambers of the braking pressure generator when slip control commences.